1. Field of the Invention
The present invention relates to an apparatus for digital correction which is for use in a color television receiver set and more particularly to a digital image correction apparatus which can automatically perform various kinds of image corrections.
2. Description of the Prior Art
In a video projector which performs widening projection on the screen by using three projector tubes for emitting light of three primary colors, incident angles, upon the screen, of light from the projector tubes (hereinafter referred to as converging angles) are in general different from each other, causing such defects as color aberration, focus error, deflection distortion and luminance change on the screen. Various corrections of these defects are effected by adjusting the magnitude and shape of analog correction waveforms which are in synchronism with the horizontal and vertical scanning periods but such a method suffers from poor correction accuracy. In addition, shifts on the screen are visually observed to make various corrections manually and disadvantageously the adjustment is time-consuming. Under the circumstances, a digital convergence apparatus capable of effecting highly accurate convergence as disclosed in JP-B-59-8114 has been proposed and digital convergence as disclosed in JP-A-55-61552 has also been proposed for automatic correction.
A conventional image correction apparatus will now be described. The conventional image correction apparatus is illustrated, in block form, in FIG. 18. In a video projector comprised of a projection display 47 and a screen 54, convergence correction circuit 1, luminance correction circuit 2, focus correction circuit 3 and deflection linearity correction circuit 4 are corrected by displaying on the screen pattern signals suitable for various corrections and which are generated from a pattern generator 7, visually extracting shift amounts and change amounts from the displayed pattern signals to provide correction data, and manually operating a manual adjuster 5 in accordance with the correction data.
Since in this manner various corrections are effected manually through visual observation, various image corrections can be effected with high accuracies.
With the conventional image correction apparatus having the above construction, however, various kinds of correction data for color aberration, focus error, deflection distortion and luminance change at individual adjustment points must be input, raising a problem that the adjustment is very time-consuming.